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Appendix IL


surface speed constant for various-sized drills. The horizontal
feed to saddle E is given by the gear on the left at B ; and the
driving gear consists of mitre wheels c and a long Marlborough
wheel D, thus permitting the tool to be set to any arranged depth.
The slide F, carrying the tool spindle, may be adjusted to give
the depth required, by means of spindle G, upon which is a small
pinion gearing into a rack on the back of the slide. The table
has the usual setting adjustments, and a hand feed is supplied
at H. The form of drill is shewn at j, which first makes a hole
of the proper depth, and is then traversed horizontally ; but if the
slot be very deep the work must be done in stages. (See p. 1019.)

jR. 775. Notes on Milling.—When work is being fed to a
milling cutter, the direction of motion of the work must be the
reverse of that of the cutting tooth. If this precaution be not
taken, the cutter will ride upon the work with great pressure, and
its teeth be broken. Thus in the left view, Fig. 181, the work

should be fed from left to right. Further, when using a helical
cutter, Fig. 181, the direction of helix must be such as to force
the cutter on and not off the spindle.

Heavy Milling Machines.—Milling is being more and
more adopted for repetition work. The mechanism of the Maxim
gun, for instance, is all but automatically turned out, by milling
machines of the pattern on Plate XII., intricate wavy sections
being cut by gangs of mills, or several cutters strung on one
4>indle. A not less interesting development is that of the heavy